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I know Android has some sort of connectivity measurement, because when there's connectivity the wifi or phone network icons will turn either green or blue, depending on the Android version.

In my opinion, this measurement isn't perfect, because although it will indicate accurately the absence of connectivity (e.g., lost wifi connectivity), it is not so accurate when the phone is connected to the Internet: at work, my Defy running Cyanogen 9 (Android 4.0.4) has icons that are always gray, no matter what, even when the connection is obviously up (see image below).

I wonder how, exactly, Android measures the connectivity status. Is it by performing a ping or other sort of probing of a server? By listening to a port? By testing if some protocol is enabled? Or what? This accepted answer to a closely related question doesn't seem to answer it.

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That Brazilian Guy
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    I'm not sure I understand how your situation is differnt than the other questions. The second question in particular describes the exact same symptoms. The Internet works, but the icons are gray because the icon color is only an indication of your connection to Google's services, nothing else. It could be that your office network is somehow restricting your access to Google's services, but not the Internet at large. We'd probably need more information to make that determination, though. – eldarerathis Oct 13 '13 at 21:09
  • @eldarerathis The accepted answer says "the phone is connected to Google services", but it means nothing to me. Is there a specific server it contancs? A specific protocol? Port? What? – That Brazilian Guy Oct 13 '13 at 22:22
  • I have now completely rewritten my question. I believe it's more clear now, and hopefully won't be closed as a duplicate. – That Brazilian Guy Oct 13 '13 at 22:30
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    As it now is a completely different question, we should all go delete our comments, answers, votes, whatevers. Unfortunately, at least for the last two items that's not so easy; so maybe next time you consider starting over with a new question and delete the old one. Changing a question this drastically when there are already answers might make the answerers (and commenters) look stupid ;) – Izzy Oct 13 '13 at 23:53
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    See also How do I make Android consider my WiFi Access Point as valid (blue?) which mentions opening tcp-udp port 5228. Or What Android versions have captive wifi detection? which has links to some of the code – GAThrawn Oct 14 '13 at 14:35
  • @GAThrawn: Amazing! That's really close of what I wanted, specially the first link. Thanks for including even the captive portal detection, going beyond the original question. If you elaborate it just a little bit more and turn it into an answer, I'll accept it! – That Brazilian Guy Oct 14 '13 at 16:12
  • Note: As of Android 4.4 (at least in the unmodified version) the icons will always be white. You need to open the settings pull-down menu to see if you have a "good" connection. – ale Dec 01 '13 at 17:19

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All of the information about it is pretty vague. Probably because they don't want people attacking a particular Google server.

For instance, the Samsung Galaxy Tab 10.1 owners manual has this to say:

Note: Network status icons turn blue if you have a Google Account added to your tablet and the tablet is connected to Google services for syncing your Gmail, Calendar events, contacts, backing up your settings, and so on. If you do not have a Google Account or if, for example, you are connected to a Wi-Fi network that is not connected to the Internet, the network icons are gray.

ale
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